It is known to provide agricultural machines, especially harvesting threshers, mowers, field harvesters and field choppers, as well as row-crop harvesting machines with automatic guidance systems for enabling the machine to follow a predetermined path along a guideline which can either be a stand of uncut crop or a row of crop material among the swath to be harvested.
Crop rows are seldom perfectly straight and, or course, have configurations which depend upon the paths of the plow, the seeding machine and other apparatus which has been used before emergence of the crop. In contour farming, for example, the rows of crop are hardly ever straight and may even have intricate patterns. Prior to the advent of automatic devices for properly positioning the harvesting head of the machine to follow the contours of the row, the operator of the machine was occupied full time in steering the apparatus along the desired harvesting line.
With the development of lateral guidance systems, i.e. automatic steering controls for harvesting machines, the operator can be concerned less with guiding the machine along the proper path and more with the effective functioning of the increasingly complicated apparatus. These controls generally comprise a device, e.g. a hydraulic cylinder, coupled to the steering mechanism of the vehicle, a sensor for following the row of crop to be cut or a stand of crop material alongside a previously cut swath, and means responsive to the sensor for operating the automatic steering control to maintain the vehicle in a proper path along this line.
Thus, the automatic steering of agricultural machines along a predetermined guideline, for example, a stand of crop or a row of stalks, is known in the art. The sensing device produces a signal which can be applied to a controller, e.g. a comparator, so that the output signal of the latter is applied to a hydraulic cylinder or other positioning element (e.g. a servomechanism), thereby correcting the position of the automatic steering device to follow deviations of the guideline from a previous orientation.
One of the problems with such systems, especially when the sensing element is an arm or finger which is deflected by the crop material along the guideline, is that this sensing element frequently encounters individual stalks which are out-of-place, i.e. stalks which are bent over, which may have grown out of the row, or which are pieces partially broken from a stalk properly growing in the row sensed by the arm or finger.
Since such out-of-place stalks are frequently stable, they deflect the sensing arm and cause an undesired correction response of the apparatus, especially where the out-of-place stalk is at some distance from the line to be sensed. As a result of the undesired or excessive corrections in the direction of movement of the machine, crop material may be uncut or the swath being cut may be given an undesired contour which can make inconvenient the cutting of adjacent swaths or rows.
Another disadvantage of conventional devices is that, when the sensor is positioned on the head of the harvesting machine, it is frequently soiled and rendered inoperative in conventional systems.